1. Field of the Invention
This invention relates to a shoe sole having a jointed section that expandable in length in a jointed area between a front sole and a rear sole, and at least one adjustment means with a spindle running approximately in a direction of a longitudinal axis of the sole in such a way that, in one direction of rotation of spindle of the adjustment means, the front and rear sole are moved toward one another and in an opposite direction of rotation of the spindle of the adjustment means, the front and rear sole are moved away from one another.
2. Description of Related Art
A shoe sole of the type to which this invention is directed is known from U.S. Pat. No. 4,944,099.
The adjusting spindle projects over the rear edge of the heel. In the area of the rear heel wall, it has an annular groove into which a guide plate that is inserted into the heel wall engages. With the aid of the guide plate and the annular groove of the adjusting spindle, the spindle can be mounted rotatably and immovably in the heel wall. When the adjusting spindle rotates via a head that projects over the rear edge of the heel, the rear section of the front sole is drawn into the heel or pulled back out from the latter depending on the direction of rotation. As a result, the size of the shoe can be continuously adjusted.
When running, as is generally known, the heel is stressed at its lower edge with maximum step-down pressure. High stressing of the heel material therefore occurs in the area of the guide plate. As a result, the adjusting spindle that runs through the entire heel is subjected to extreme bending stress, especially in the rear area, when stepped on in this way. The jointed area of the front sole is not configured in an expandable manner in this sole design.